With the newly released version of VMware Fusion 12.0 I'm having the same problem I did with the Technical Preview in macOS Big Sur Beta 6.
When starting a Windows 10 x64 virtual machine, I receive the following error message:
Could not connect 'Ethernet0' to virtual network '/dev/vmnet8'.
More information can be found in the vmware.log file.
Virtual device 'Ethernet0' will start disconnected.
Has anyone found a solution to restoring internet availability in the guest virtual machine?
Cheers